The present invention relates to the control of a coupling device between an input shaft driven by a motor and an output shaft that can transmit a maximum torque based on the position of an actuator of the coupling device, in accordance with a law of behavior of the coupling means.
A hybrid traction drive—for example, composed of a heat engine coupled to an electrical machine via a clutch, and which drives an input shaft of a gearbox, which itself drives the wheels of a motor vehicle—must have torque control for the engine members, i.e., the heat engine and the electrical machine, in order to best meet the driver's demand, expressed in terms of torques to apply at the wheel.
In a hybrid traction drive, the torque to apply at the wheel is distributed between the heat engine and the electrical machine based on the specific operating conditions of the vehicle, in particular to optimize the energy consumption of the traction drive.
In order to control this assembly, the distribution of torque must be varied between the heat engine and the electrical machine. This entails being able to couple and decouple the heat engine and the electrical machine with a coupling means between the heat engine and the electrical machine. This coupling member, which is generally a friction clutch, must be controlled in such a way that the torque transmitted by the clutch is precisely ascertained, at least during periods when the clutch is sliding.
Conventional traction drives also have coupling/decoupling means that can be controlled. When the coupling/decoupling means are controlled, the transmitted torque must also be controlled, particularly upon starting or changing gearbox ratios.
In order to properly control such a device, one must precisely formulate a clutch operation law that can determine the relation between the position of an actuator of the clutch and the maximum torque that the clutch can transmit during the time it is sliding.
This is why control devices for such traction drives use a law of behavior for the clutch that yields the relation between the position of the clutch command member and the maximum torque that said clutch can transmit. But such laws are progressive over time for various reasons, particularly because the clutch heats up when it is used frequently, or because of wear on it or deviations in manufacturing characteristics.
The progression in the laws of behavior of the clutch are taken into account by establishing procedures to determine the biting point in particular: that is, the position of the command member that allows contact to begin between the two clutch plates.
However, this approach has the drawback of being rather imprecise. Particularly, it is observed that the procedure for determining the biting point is highly sensitive. For this reason, in actual vehicle use, using such a procedure leads to unacceptably rough operation, with the result that it is preferable to retain laws of clutch behavior without factoring in the variations in the biting point. However, it is observed that the clutch control is highly irregular with this approach as well.